Influence of Pigging Velocity on the Wax Removal Process in Subsea Pipelines

Abstract

Wax deposition has been a significant concern in flow assurance. Mechanical pigging is the most common technique used to remediate wax deposition in subsea pipelines. Although researchers have revealed the wax removal process of pipe pigs, it is still unclear whether the pipe pig speed affects the pigging process. Due to a lack of understanding of the wax removal process, the field pigging operation is mainly reliant on empirical rules, resulting in frequent blockage accidents. In this work, the effect of pipe pig speed on the pigging process of cup and disk pigs was investigated using the in-house pigging facility. The experimental results show that the pigging process of both pipe pigs at high and low speeds can be divided into four parts. However, the wax breaking force (WBF) is approximately 2–3 times greater at high speed than at low speed. Also, the WBF of the disk pig is higher compared to the cup pig under the same pigging conditions. The mechanism behind this phenomenon is because of the rheological features of wax deposits. Since the wax deposit exhibits rheomalaxis elasto-viscoplasticity, it is exposed to a larger shear rate at high pipe pig speed, which leads to increased dynamic yield stress of the wax deposit. Furthermore, the difference in WBF between cup pigs and disk pigs results from the geometric characteristics of the pipe pigs. This work can serve as a qualitative guide for on-site pigging operations of subsea pipelines.